Re: IORING_OP_POLL_ADD/IORING_OP_POLL_REMOVE questions

[Olivier Langlois <olivier@trillion01.com>]

On Wed, 2021-05-05 at 23:17 -0400, Olivier Langlois wrote:
> Note that the poll remove sqe and the following poll add sqe don't have
> exactly the same user_data.
> 
> I have this statement in between:
> /* increment generation counter to avoid handling old events */
>           ++anfds [fd].egen;
> 
> poll remove cancel the previous poll add having gen 1 in its user data.
> the next poll add has it user_data storing gen var set to 2:
> 
> 1 3 remove 85 1
> 1 3 add 85 2
> 
> 85 gen 1 res -125
> 85 gen 1 res 4
> 
Good news!

I have used the io_uring tracepoints and they confirm that io_uring
works as expected:

For the above printfs, I get the following perf traces:

 11940.259 Execution SVC/134675 io_uring:io_uring_submit_sqe(ctx:
0xffff9d3c4368c000, opcode: 7, force_nonblock: 1)
 11940.270 Execution SVC/134675 io_uring:io_uring_complete(ctx:
0xffff9d3c4368c000, user_data: 4294967382, res: -125)
 11940.272 Execution SVC/134675 io_uring:io_uring_complete(ctx:
0xffff9d3c4368c000)
 11940.275 Execution SVC/134675 io_uring:io_uring_file_get(ctx:
0xffff9d3c4368c000, fd: 86)
 11940.277 Execution SVC/134675 io_uring:io_uring_submit_sqe(ctx:
0xffff9d3c4368c000, opcode: 6, user_data: 4294967382, force_nonblock:
1)
 11940.279 Execution SVC/134675 io_uring:io_uring_complete(ctx:
0xffff9d3c4368c000, user_data: 4294967382, res: 4)

So, it seems the compiler is playing games on me. It prints the correct
gen 2 value but is passing 1 to io_uring_sqe_set_data()...

I'll try to turn optimization off to see if it helps.

thx a lot again for your exceptional work!